Gear generating tool



Nov. '7, 1939.

D T HAMILTON GEAR GENERATING TOOL Original Filed April 17, 1934 2Sheets-Sheet l Nova 7, 1939. D. T HAMILTON GEAR GENERATING TOOL OriginalFiled April 17, 1934 2 Sheets-Sheet 2 i/*7 W Z W atented Nov. 7, 1939 l@J'lhfifitl GEAR GENERATING TDOL Douglas E. Hamilton, Springfield, Vt.,assignor to The Fellows Gear Shapcr Company, Springfield, Vt, acorporation oi Vermont Original application April it], 1934, Serial No.720,954., Divided and this application Febru ary ll, 1936, SerialNo.62,285

2 Claims. (Cl. ltd-95) This invention relates to the art of generatingelement in comparison with said patent, as they and cutting gears by theagency of a cutter out during every stroke in each direction inequippedwith peripheral teeth of which the outstead of returning idly onalternate strokes. lines are similar to the outlines of gear teeth Theinvention also contemplates improve- 5 and the cutting edges areprovided at the intermerits in cutters adapted for operation on helical5 sections of the sides of such teeth with planes, gears. The teeth ofsuch cutters have heretofore transverse to the axis of the cutter, whichdealways been made with convergent sides for fine the ends of the teeth.Such cutters as clearance, as well as being generally helical inheretofore made have been of unlike charactercomplement to the gears tobe produced. Their l0 istics at opposite ends because of the necessityof opposite sides are therefore of different helical providing'cuttingclearance. That is, the oppoleads. They are usually sharpened in planesor site sides of each tooth have been convergently lines normal to themedian helices of the teeth, in inclined toward one another away fromthe cutorder to make the clearance angles equal on both ting end. Thusthe cutting end of the tooth is sides. Difficulties of no smallmagnitude are inthe larger end and its contact with the work is volvedin producing such helical cutters with limited to the cutting edges, asis required for tooth face curvatures such that edges which are doingsatisfactory work. Such cutters, when formed by substantially normalintersecting dull, are sharpened by grinding off the face at the planeswill yet generate tooth curves in the work large end; which causes theteeth eventually to which are of the correct form in planes perpenbecomeprogressively narrower, owing to the dicular to the axis of the work.And the sharpto clearance. inclinations of their opposite faces. eningof such helical cutters involves a separate Compensation for suchreduction in width must operation for each tooth and indexing of thethen be made in order that the teeth may be cut cutter betweensharpening operations. with standard, or prescribed, width in the worlr.The object and accomplishment of the present When a cutter of involutetooth formation is used invention has been to provide a cutter havinglit for cutting involute gears, this compensation may adequate clearanceangles on both sides of its be made by shortening the center distancebeteeth, but of which the teeth are of uniform di tween cutter and work;but this is not possible mensions in all planes perpendicular to itsaxis, incutting teeth of other forms or in cutting some whereby nochange of tooth dimensions (other so classes of gear elements even withan involute than length in the axial direction) results from so cutter.sharpening; which can be sharpened on both Another mode of compensationwhich is availends, and all the teeth of which can be sharpened able forcutting teeth and analogous lobes or in a continuous grinding operationwhether the projections of all profiles or outlines, is disclosed cutteris designed for generating straight gears 5 in the patent to Edward W.Miller, No. 1,802,181, or helical gears; and one which can be made atApril 21, 1931, and comprises turning the cutter a lower cost than gearshaper cutters heretofore from side to side, between cutting strokes, adisp ced- A rel je which is accomtance equal to the difference betweenthe width plished by realization of the f r in j ct of the cutter toothand the width of the space is to avoid any change in the relationship ofthe required to be generated in the work, so as to cutter to the work inconsequence of sharpening. 40 cut alternately on opposite side edges ofeach The invention claimed herein is a novel gear tooth. This procedureavoids the difiiculties shaper cutter having the characteristicshereinconsequent on changing the center distance, but before referred toand more fully described in the as the cutter used therein has edges onone end following spe n This Subject m r was '45 only, it requires moretime for completion of the originally disclosed in my prior copendingappli- 1 work, other things being equal, than is required cation filedApril 17, 1934, Serial No. 720,954, of when both sides of a full widthcutter tooth act at which the present application is a division. Allgnca of the principles and novel features which con- Cutters whichembody the present invention stitute the invention are intended to beprotected are designed to be used with angular movements in a scopecovering externally toothed cutters 50 about their axes after eachstroke according to adapted to generate or form external or internal theprinciple of the above named patent, but gears and similar machineelements with straight are provided with cutting edges at opposite sidesor helical teeth, and internally toothed cutters of their teeth and atrelatively opposite sides of for generating or forming either helical orsuch opposite ends. Their use shortens the time straight toothedexternal gears and the like. 55

In the drawings which accompany this speciflcation,-

Fig. 1 is a diagrammatic view illustrating the general principles of amachine suitable for shaping gears with the aid of my novel cutter;

Fig. 2 is a side elevation of the invention embodied in a cutterdesigned to generate helical gears;

Fig. 3 is a similar view of a gear generated by the cutter shown in Fig.2;

Figs. 4 and 5 are diagrammatic views showing the alternate action, onits opposite strokes, of a cutter designed for generating helical gears,being represented as sectional views taken re- 5 spectively on lines 4-4of Fig. 8, and 55 of Fig.

figs. 6 and 7 are views similar to Figs. 4 and 5 respectively, showingthe action of an equivalent cutter designed to generate the teeth ofstraight spur gears, or equivalent internal gears;

Figs. 8 and 9 are fragmentary sectional views, in pla'nes perpendicularto their axes, of a cutter in action upon a helical gear; the planes inwhich such sections are taken being indicated by the lines 88 of Fig. 4,and 99 of Fig. 5, respectively;

Fig. 10 is a side elevation of a cutter made according to the principlesof this invention for cutting gears with straight teeth;

Fig. 11 is an elevation of a gear generated by the cutter of Fig. 10;

Fig. 12 is an outline view of a form of cam suitable to effect theincrement oscillation of the cutter which causes its teeth to act onalternately opposite sides during strokes in opposite directions.

Like reference characters designatethesame parts wherever they occur inall the figures.

In these figures. the letter C designates the novel cutter of thisinvention designed for generating helical gears, and C (Fig. 10)designates an equivalent, interchangeable cutter designed for generatinggears with straight teeth. W is an illustrative helical gear produced bythe cutter C; and W (Fig. 11) an illustrative spur gear produced by thecutter C. In preparation for carrying out the gear cutting operation,the cutter is mounted on one end of a cutter spindle l, and the workpiece on a work spindle 2. One of these spindles is then reciprocatedendwise while both are rotated simultaneously in such directions andspeeds as to give relative rotational effects to the cutter and worksimilar to those of a pair of mating gears running in mesh with 55 oneanother.

The opposite side faces of the cutter teeth are outlined with the samecurvature (in all planes perpendicular to the axis of the cutter) as theteeth of a standard gear in any desired system 60 of gearing, or anyoutline conjugate or complemental to the forms desired to be cut in thework. That is, if involute gears are to be made, the cutter tooth facesare involute curves; or for cutting cycloidal gears they are cycloidalcurves,

5 etc. They may also be modified from standard curvature, if desired,according to principles heretofore known and described in prior patent,to cause quiet meshing of the gears which are made by their use. Theseteeth, however,are

70 narrower on the operating pitch circumference than the tooth spacesdesigned to be cut in the work pieces (and also narrower than the spacesbetween them on the same circumference, in the case of cutters designedto finish standard gears and the like of which the teeth and spaces havesubstantially the same width on the operating pitch circumference)wherefore they cut by the edges at one side only of their teeth at atime.

All the cutters embodying the invention whether made for cutting instraight or helical paths, differ from the gear shaper cutters hithertoused in that their teeth are exactly uniform as to dimensions andoutlines in all planes perpendicular to the axis of the cutter, and aresharpened at both ends. The teeth of all, even those for cuttingstraight toothed gears, are helical; but the helix angles of both sidefaces are equal and of the same hand. That helix angle, in the case ofcutters designed for making straight toothed gears, is only the amountof the clearance angle, and may be as small as one degree from a lineparallel to the axis; and, of course, may be slightly or considerablygreater. In the case of cutters for helical gears, it is the helix anglecomplemental to that of the gear to be cut plus orminus a suitableclearance angle. In terms of helical lead (which is the axial distancebetween successive convolutions of a helix, and is a constant for agiven regular helicoidal surface at all distances from the axis of thehelicoid), the lead of the cutter teeth is shorter than that of theteeth to be generated.

Referring to the helical cutter shown in Figs. 2, 4, 5, 8 and 9, eachtooth t has helicoidal side faces 12' and t ,'which are equidistant fromone another at corresponding points in all planes perpendicular to thecutter axis, and has cutting edges t and 1! formed respectively by theintersection of the end face t with the side face t and the intersectionof the end face i with the side face t. The helix angles of the faces tand t are equal to the helix angles of the gear tooth faces 9' and o ofthe work piece, minus the clearance angle of one degree (more or less).Hence the cutting edge t is the only part of the cutter tooth capable ofengaging the gear tooth face 9 and the edge t is the only part of thecutter tooth which can engage the gear tooth face 9'.

In the course of the downward stroke of the cutter (considered withrespect to Figs. 4 and 5), tooth t is brought so that its edge t cutsthe face 9' of the work piece; and corresponding edges of other cutterteeth act upon relatively corresponding parts of other teeth of the workpiece, while all other parts of the cutter are out of contact. When thecutter has been carried clear of the work, 'as shown by the dotted lineposition td, it is given a slight incrementalrotation about its axissufiicient to bring the cutting edge t into action on the face 9 of thework; and it cuts on the following up stroke, while edge t is shiftedclear of the face g Arriving at the upper position tu, the cutter isshifted incrementally to the opposite side, and the edge t comes intoaction again on the next down stroke.

Thus on each down stroke, the cutter acts through one edge only of itsoperative teeth at the lower end thereof, and on each up stroke it actsby means of the opposite edge at the upper end of the tooth. All of thecutter teeth which have penetrated into the work piece act inessentially this manner; while different teeth are successively cominginto and out of action by virtue of the continuing generating rotation.

The cutters for making straight teeth operate in exactly the same way.Their only difference from helical gear cutters is in the helix angle oftheir teeth. This is made plain by comparison of Fig. 10 with Fig. 2,and of Figs. 6 and 7 with Figs. 4 and 5 respectively. Accordingly I havedesignated the cutting edges of the tooth shown in Figs. 6 and 7 by thesame reference characters as those used in Figs. 4 and 5. A generalstatement applicable to both types of cutter and both modes of gearcutting herein described is this:--The helical leads of opposite sidesof the respective cutter teeth are equal to one another, and are shorterthan the lead of the path in which the cutter teeth travel in cutting,by an amount sufficient to provide the desired side clearance. Thestraight line path in which the cutter moves when finishing straightspur gears is here considered as one having a lead of infinite length.

It will be noted that in every case the cutting edges are acute angles,and that the obtuse angle edges between the side and end faces of theteeth are not brought into action at all. This makes it unnecessary tosharpen the teeth of the helical cutter in such a way as to form anacute angle edge at the corners designated t and t Thus the cutters maybe sharpened by grinding off the end face in a continuous sweep,'eitherin planes square to the axis, or on a dished conical or sphericalsurface, if desired, for additional top rake. If the angle at the edgest and t is so sharp as to leave insufficient strength at these edges,the end faces t and t may be beveled in known manner.

Gearshaping machines by which my cutters may be operated with the effectabove described are already in existence and are disclosed in the beforementioned Miller Patent No. 1,802,181. I have illustrated herein theprinciples of said patented machine, in a diagrammatic way by Fig. 1.Typical means for reciprocating the cutter spindle l are designated by acrank pin 3 acting through a link 4, rocker arm 5, gear segment 6, andrack teeth I encircling the spindle in mesh with said segment. Means forrotating the cutter and work spindles in harmony with one another aretypified by a worm gear 8 on the cutter spindle in mesh with a worm 9, aworm gear Ill on the work spindle in mesh with a worm II, andtransmission gearing and shafts between these two worms and-the mainshaft l2. An operative train of such mechanism, including changeablegears for varying the speed ratio, in the train of the work spindledrive, are indicated by broken lines.

The side movements of the cutter, previously described as shifting itsactive teeth between cutting positions at alternately opposite sides,are eflected by incremental oscillations superimposed upon the normalrotation of the cutter spindle. These oscillations may be caused byshifting the worm 9 endwise in alternately opposite directions by a caml3 and a spring ll respectively; the cam actingthrough a lever l5 and astud l6 carried thereby against the end of the worm shaft, and thespring reacting against an opposed abutment on the frame structure. Thecam is shown as being driven from the main shaft by chain l8, gearingl9, shaft 20, and gearing 2| in proper timing with the reciprocations ofthe spindle so that the cutter is shifted with the effect previouslydescribed at the times when it is clear of the work. It is to beunderstood that the directions of these lateral incremental movementsare relative to the rotation and positions of the work. and notabsolute. 'That is, the shift of the cutter in one direction maybe atemporary retardation or arrest of its normal rotation rather than areversal of such rotation.

In cutting straight toothed gears, the cutter spindle has only themovements of reciprocation, rotation, and incremental oscillation abovedescribed; and rotation is transmitted to it from the driving gear 8through guides which permit endwise sliding movement and. have contactfaces parallel with the axis. But for cutting helical gears, the cutterhas still another oscillative movement, in relatively oppositedirections on opposite strokes, effected by making such guides ofhelical formation with such a lead that the paths of the active cutterteeth conform with the helix angle of the gear teeth to be produced. Theprinciples and essential characteristics of guides suitable for thispurpose which I employ are shown in the patent to E. R. Fellows, No.676,227, June 11, 1901. V

The same cutter principles are applicable also to internally toothedcutters for forming externally toothed elements inthe manner disclosedby the patent to E. W. Miller No. 1,953,969, April 10, 1934, and formaking conjugate external teeth by the molding generating process.Internal cutters thus modified have the same characteristics beforedescribed of helical teeth with equal lead and of the same hand on bothsides, end

faces substantially or nearly parallel to one another and perpendicularto the cutter axis, and cutting edges at the acute-angle intersectionsof both end faces and the opposite side faces .of all the teeth.

Such cutters, external as well as internal, are useful particularly forfinishing gears and the like which have previously been cut to a more orless close approximation to prescribed dimensions but have a certainamount of material still to be removed. 1

Nothing in the foregoing description of typical operating means is to beconstrued as limiting the use of the new invention to that situationonly wherein the cutter is reciprocated and incrementally oscillated. Onthe contrary, the invention is equally applicable to situations whereall of these motions are imparted to the work spindle, or they areshared between the cutter and work spindles.

What I claim and desire to secure by Letters Patent is:

1. A cutter of the gear shaper type having a geometrical axis and teetharranged in a series surrounding said axis, the corresponding end facesof all the teeth being in the same surface of revolution substantiallyperpendicular to the said axis, and the opposite end faces of all theteeth being in another surface of revolution also substantiallyperpendicular to said axis, the opposite side faces of each tooth havinghelical curvature of the same lead, and the acute angle intersections ofsaid side faces with the end faces forming cutting edges, the width ofthe teeth on the operating pitch circumference of the cutter being lessthan the corresponding width of the spaces to be cut in the work.

2. A gear finishing cutter having helical teeth arranged in a curvedseries surrounding an axis. with their end faces substantiallyperpendicular to said axis, each tooth being of equal width in allplanes perpendicular to the axis, and their width on the operating pitchcircumference of the cutter being less than the width of the spaces tobe cut in the workpiece, and the acute angle intersections of the sideand end faces of the teeth being cutting edges.

DOUGLAS '1. HAMEJTON.

